The present invention relates to an MOCVD (Metal Organic Chemical Vapor Deposition) method of a tantalum oxide film in a semiconductor processing system, and more specifically to a technique of forming, e.g., a gate insulating film, capacitor insulating, or the like of a semiconductor device. The term "semiconductor process" used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD (Liquid Crystal Display) substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
In order to manufacture semiconductor devices, film formation and pattern etching are repeatedly applied to a semiconductor wafer. As semiconductor devices are becoming more and more highly miniaturized and integrated, demands on film formation have become stricter. For example, very thin insulating films, such as capacitor insulating films and gate insulating films are still required to be thinner and to be more insulating.
Conventionally, silicon oxide films and silicon nitride films are used as the insulating films. In recent years, however, it has been proposed to form the insulating films from materials having even higher insulating properties, such as a metal oxide, e.g., tantalum oxide (Ta.sub.2 O.sub.5). The film of this material can be formed by means of MOCVD, i.e., using a vaporized metal organic compound.
To form a tantalum oxide film by means of MOCVD, a metal (tantalum) alkoxide, such as Ta(OC.sub.2 H.sub.5).sub.5 (pentoethoxytantalum: PET) is used as a raw material liquid. The raw material liquid is made to bubble by e.g., nitrogen gas, or vaporized by a vaporizer set at a vaporizing temperature, to be in a gaseous state, and is supplied to a process chamber preset to have a vacuum atmosphere. At the same time, an oxidizing gas, such as oxygen, is supplied to the process chamber. The supplied raw material is decomposed to offer a film forming material on the surface of a semiconductor wafer heated to a predetermined process temperature. With this film forming material, a tantalum oxide (Ta.sub.2 O.sub.5) film is formed on the surface of the semiconductor wafer by means of deposition.
As semiconductor device design rules have become stricter, the required thickness of tantalum oxide films is now about 10 nm at max. Tantalum oxide films grow at a deposition rate of about 150 nm/min when a deposition temperature is about 600.degree. C. Accordingly, where tantalum oxide films having a thickness of about 10 nm have to be formed with high accuracy, a low deposition temperature of about 400.degree. C. is used to reduce the deposition rate. In the case of using such conditions for forming tantalum oxide films, however, the present inventors have found a problem in that the surface of the tantalum oxide films becomes uneven, i.e., the degree of surface roughness is higher and the surface morphology is degraded, thereby deteriorating the electric properties of the film.